1. Field of the Invention
The present invention relates to an engine generator suitable for preventing temperature rise in a power control unit of the generator.
2. Description of the Related Art
Engine generators are used outdoors as general-purpose power supplies. In recent years, there has been an increased demand for outputs of such engine generators to be controlled by a power control unit such as an inverter.
Such a power control unit includes a circuit board on which an electric circuit for controlling power supplied from an engine generator is provided. When the electric circuit is supplied with a large electric current, the board produces a large amount of heat. Therefore, it becomes necessary for the thus-heated board to be cooled down.
Technique for cooling the above-described circuit board is known from, for example, Japanese Utility Model Laid-Open Publication No. SHO-63-171632 entitled xe2x80x9cPORTABLE ENGINE GENERATORxe2x80x9d and Japanese Utility Model Post-Exam Publication No. HEI-6-11535 entitled xe2x80x9cELECTRONIC COMPONENT UNITxe2x80x9d.
The engine generator disclosed in the Publication No. SHO-63-171632 includes an end surface cover forming therein openings for taking in air, and a box member having an outer surface facing towards the end surface cover. The box member accommodates therein a control circuit unit. On the cuter surface of the box member, there are provided a plurality of heat releasing fins. The adjacent fins define an intake passage therebetween. Air taken into the openings flows through the respective intake passages. With this arrangement, when the control circuit unit generates heat, the heat is transmitted to the box member. The box member is cooled by the air passing through the intake passages as described above.
The Publication No. HEI-6-11535 discloses an electronic component unit including a case of aluminum accommodating therein a base sheet on which plural electronic components are mounted. The case is filled with hardened resin to cover the base sheet. With this arrangement, heat generated by the base sheet is released by means of the case having improved thermal conductivity.
As disclosed in the Publication No. SHO-63-171632, the air is directed against the outer surface of the box member to thereby cool the box member having the control circuit accommodated therein. However, when the engine generator supplies large power to thereby cause the control circuit unit to generate a large amount of heat, the box member can not be sufficiently cooled because the outer surface of the box member having the fins provided thereon provides limited area. As a result, the control circuit unit is difficult to cool.
Also, when the electronic components as disclosed in the Publication No. HEI-6-11535 provide large power to thereby generate a large amount of heat, it is required that the surface of the case serving as a heat releasing sheet have an enlarged area or that a separate heat releasing sheet of large size be added to the base sheet such that the case can effectively release the heat therefrom. In such a case, however, the electronic component unit is inevitably made large in size.
An object of the present invention is to provide an engine generator including a power control unit and a heat releasing member which is formed from an existent member to thereby downsize the unit and which is disposed to effectively cool the unit to thereby prevent the temperature of the unit from rising.
According to an aspect of the present invention, there is provided an engine generator carrying thereon an engine and a generator driven by the engine, the engine generator comprising: a cooling fan mounted on a rotational shaft of the generator; a fan cover for covering the cooling fan; a power control unit including an aluminum base sheet forming thereon a power control circuit for controlling an output from the generator; the fan cover being made of die-cast aluminum alloy; the power control unit being attached to the fan cover with a surface of the aluminum base sheet intimately contacting an outer surface of the fan cover.
Heat generated by the control circuit unit is transmitted to the fan cover made of die-cast aluminum alloy. The heat is then released from the fan cover. The fan cover intimately contacts the surface of the aluminum base sheet of the power control. The cooling fan directs cooling air against the fan cover.
Since the surface of the aluminum base sheet intimately contacts the fan cover, the heat generated by the power control circuit can be efficiently transmitted to the fan cover. In addition, the cooling fan directs cooling air against the fan cover during the operation of the power control unit. Thus, the heat can be effectively released from the fan cover to thereby prevent temperature of the power control unit from rising.
The fan cover for covering the cooling fan serves as a heat releasing member for the power control unit. This eliminates the need to provide the power control unit with a separate heat releasing member of large size such as the heat releasing fins. Thus, it becomes possible to downsize the power control unit as well as to make small the number of parts forming the engine generator. Consequently, the cost of the engine generator can be reduced.
In a preferred form of the invention, the fan cover has a thick mounting portion formed thereon, the mounting portion having a flat outer surface to be attached to the surface of the aluminum base sheet.
The heat generated at the unit is transmitted from the surface of the aluminum base sheet of the unit to the entire fan cover through the thick mounting portion having the flat outer surface.
Since the mounting portion of the fan cover is made thick to thereby increase heat capacity thereof, the transmission of the heat to the fan cover is improved. It thus becomes possible to prevent the temperature of the unit from rising.
Moreover, the flat mounting portion is advantageous in that the intimate contact between the unit and the surface of the aluminum base sheet can be readily effected, and in that the mounting portion can be easily formed.
In a further preferred form of the present invention, the generator has a flywheel structure including an outer rotor fixed to the rotational shaft, the outer rotor having the cooling fan mounted thereon, and the fan cover for covering the cooling fan has a cylindrical configuration and is opener at opposite end portions either of which is secured to the engine and discharges cooling air therefrom.
The cooling fan directs cooling air along the cylindrical fan cover towards the engine to thereby cool the engine.
The cooling air is continuously taken into the fan cover of cylindrical configuration. The fan cover has the inner surface exposed to the cooling air. Therefore, heat transmitted to the fan cover can be effectively released therefrom.
In a still further preferred form of the present invention, the outer rotor includes permanent magnets, the cooling fan is formed from a centrifugal fan, the outer rotor and an inner surface of the fan cover define a passageway therebetween, and the cooling air is forced to flow through the passageway towards the engine.
The outer rotor includes the permanent magnets and the cooling fan is formed from the centrifugal fan. With this arrangement, the cooling air is directed radially outwardly from inside the cooling fan. The air is then forced to flow through the passageway, defined between the outer rotor and the inner surface of the fan cover, towards the engine.
Thus, since a large amount of cooling air is directed against the inside of the peripheral surface of the fan cover, the fan cover can be effectively cooled.
In a still further preferred form of the present invention, the power control unit is a cycloconverter unit or an inverter unit for converting an output from the generator into a power having a predetermined frequency.
The inverter unit or the cycloconverter unit converts the output from the generator into a power having a predetermined frequency.
An inverter or cycloconverter generates a large amount of heat corresponding to power loss caused when controlling a large power supplied from the generator. It was therefore difficult to reduce the size of a conventional inverter or cycloconverter unit. However, since the present invention employs the unit attached to the fan cover, the size of the unit can be reduced to xc2xdto ⅓of the size of the conventional unit.